650 THE AMERICAN NATURALIST [Vol. XLIT 



cific power of protoplasm for assimilation (in the. strict 

 sense), and leave it alone as a fundamental phenomenon, 

 but are much concerned as to the distribution of the new 

 growth in innumerable specifically distinct forms. In the 

 Chemical Section they call this class of phenomenon 

 " autocatalysis, " and a. number of cases of it are known. 

 In these a chemical reaction gives rise to some substance 

 which happens to catalyze the particular reaction itself, 

 so that it goes on and on with ever-increasing velocity. 

 Thus, we said that free acid was a catalyst to the hydro- 

 lysis of cane-sugar ; suppose now that free acid were one 

 of the products of the hydrolysis of sugar, then the ca- 

 talyst would continually increase in amount in the test- 

 tube, and the reaction would go faster and faster. Un- 

 der certain conditions this actually happens. Again, 

 when methyl acetate is hydrolyzed we normally get 

 methyl acohol and free acetic acid. This free acid acts 

 as a catalyst to the hydrolysis, and the rate of change 

 continually accelerates. Here, if the supply of methyl 

 acetate were kept up by constant additions, the reaction 

 would go faster and faster with a logarithmic accelera- 

 tion giving a curve of velocity identical with Fig. 2, A. 



For a clear manifestation of this autocatalytic increase 

 in the plant it is, of course, essential that the supply of 

 food materials to the protoplasm be adequate. 



Another case where we might look for a simple form 

 of this autocatalytic increase in the rate of conversion of 

 food materials to anabolites would be in the growth of a 

 filamentous alga, like Spirogyra. Here, as in the bacter- 

 ium, all the cells are still capable of growth. In this case 

 the food-material needed in greatest bulk is carbon, which 

 has to be obtained by photosynthesis. Some experiments 

 have been started in the Cambridge Laboratory on the 

 rate of growth of Spirogyra in large tubs of water kept 

 at different temperatures and with varying facilities for 

 photosynthesis and metabolism. Under rather depress- 

 ing conditions the Spirogyra took several days to double 

 its weight— a rate of metabolism out of all comparison 

 slower than that of bacteria. Experiments on these 



